Such batteries can be used in electric drive or hybrid automotive vehicles, or in other types of systems that have a battery on board.
In general, for these applications, very high capacity batteries are used that are capable of delivering several tens of amp hours, with a very high voltage across their terminals, for example of the order of 400 volts. In order to obtain such high voltage values, cells each having a voltage of the order of a few volts are assembled in series. These cells can constitute a module (of variable size) or the whole of the battery.
Conventionally, the cells are monitored in order to ensure that the voltage across the terminals of these cells is in the nominal voltage range of the module or of the battery. Specifically, it is advisable to check that the voltage across the terminals of a cell is not too low in order to avoid deteriorations in the cell, and it is also advisable to check that the voltage across the terminals of a cell is not too high in order to avoid both deteriorations in the cell and also fires and explosions in the cell.
Therefore, means for measuring the voltage across the terminals of the cells forming a battery are used. These measuring means are powered directly by the cell for which they measure the voltage(s). The measured voltage value is then communicated to a central processing unit, or electronic control unit, that can also send commands to means that are intended to balance a cell. For this reason, at least two separate connections are used between each cell and the central processing unit.
As will be understood, since the voltage means are powered directly by the cells or the modules, and the central processing unit is powered by other sources of electric power, it is necessary to use insulating means in each connection between the cell or the module and the central processing unit. It is also possible to use insulating means between each connection from a cell or a module to a databus communicating with the central processing unit. Optocouplers, or even magnetic galvanic isolators, are generally used in order to obtain electrical insulation.
It may be noted that many components are used, particularly two insulating means per cell or per module. The increase in the number of components renders implementation of the system more complex, and it increases the cost of battery management systems.
In view of the above, the aim of the invention is to allow a simpler battery management system to be obtained that uses fewer components and that has lower cost.